>> Check your org-ctrl-c-ctrl-c-hook
>>
>> I don't have it defined, but maybe you mean to do something else? Calling
> org-set-tags gives the same result as dos C-c C-q.

Then, `org-after-tags-change-hook'.

More generally, you can M-x toggle-debug-on-error to see more detailed
backtrace.

Ah, thanks. The only message I get is:

Symbol’s function definition is void: consult-completing-read-multiple

It's most definitely something in my setup, I just can't seem to find what :/